The present invention relates generally to measuring performance of networks, and specifically to measuring the performance of links within a local area network.
As customer requirements for rates of data delivery over Local Area Networks (LANs) increase, network installers and maintainers are increasing the rates at which data is transferred. Links in such networks commonly comprise cables and associated connectors within the network. Older cables and connectors, which may have been installed to handle 1 MHz or 10 MHz frequencies, are required to cope with 100 MHz or even 1 GHz. As frequencies are increased, signal degradation increases significantly due to, amongst other causes, frequency-dependent attenuation. Signal processing techniques are available to correct for such degradation, at least in part.
At higher frequencies, cable maintenance and diagnosis of problems, whether of older cables or of cables specifically installed for these higher frequencies, becomes significantly more demanding. Telecommunications Systems Bulletin 67 (TSB-67), issued by the Electronics Industry Association (EIA) of Washington, D.C., and the Telecommunications Industry Association (TIA) of Arlington, Va., specifies requirements that are to be met for category-5 cables used within a LAN operating under one of the Ethernet 100BASE standards. Some of the category-5 cable types covered in TSB-67 are: unshielded twisted pair (UTP), shielded twisted pair (STP), screened twisted pair (SCTP), and foiled twisted pair (FTP). TSB-67 specifies that amongst the parameters that are to be measured in determining compliance with the requirements are the physical length and the attenuation of each cable within the LAN.
Each particular type of cable has a nominal attenuation, also termed a nominal insertion loss, in dB/100 m. The nominal attenuation of UTP category-5 cable in dB/100 m is given by the equation:       Nominal    ⁢          xe2x80x83        ⁢    Attenuation    =            2.1      ·              f        0.529              +                  0.4        f            ⁢              xe2x80x83            [              dB        ⁢                  /                ⁢        100        ⁢                  xe2x80x83                ⁢        m            ]      
wherein f is the frequency in MHz. For example, the nominal attenuation of UTP category-5 cable at 100 MHz is 24 dB/100 m.
In addition to the nominal attenuation of the cable, in practice there are also xe2x80x9cflatxe2x80x9d (frequency-independent) attenuations caused by, for example, connectors or an electrical interface to the cable. Other fixed attenuations are frequency-dependent, such as are caused by magnetics (transformers) feeding the cable.
An approximate effective length (LE) of a specific cable may be defined as:                               L          E                =                                                                              Actual                  ⁢                                      xe2x80x83                                    ⁢                                      attenuation                    ⁢                                          xe2x80x83                                        [                    dB                    ]                                                  -                                  Fixed                  ⁢                                      xe2x80x83                                    ⁢                                      attenuation                    ⁢                                          xe2x80x83                                        [                    dB                    ]                                                                              Nominal                ⁢                                  xe2x80x83                                ⁢                cable                ⁢                                  xe2x80x83                                ⁢                                  attenuation                  ⁢                                      xe2x80x83                                    [                                      dB                    ⁢                                          /                                        ⁢                    100                    ⁢                                          xe2x80x83                                        ⁢                    m                                    ]                                                      ·            100                    ⁢                      xe2x80x83                    ⁢          m                                    (        1        )            
In practice, the effective length of a cable is a more useful measure than the physical length, since the effective length incorporates the actual cable attenuation in the measurement, and so gives a better measurement of the quality of the connection formed by the cable. When a link is formed by more than one cable, the effective length of the link, defined by summing the effective lengths of the cables based on equation (1), is similarly a more useful measure than the physical length.
Fluke Corporation, of Everett, Washington, produces a set of meters called a DSP-2000 for measuring parameters of LAN cables. Wavetek Corporation, of San Diego, Calif., produces a similar set of meters, called an LT-8000. Both sets of meters are operated in substantially the same manner. A cable to be tested is removed from the network, e.g., by disconnecting one end of the cable at a cable closet and by disconnecting the other end of the cable at a user""s work station. One of the meters in the set is connected to one end of the cable, and the other meter in the set is connected to the other end of the cable. An alternative method of measurement connects one meter to an end of the cable, and disconnects the other end of the cable, leaving it as an open circuit. The length of the cable is measured by finding the time taken for a pulse to travel along the cable using a direct path when two meters are used, or a reflected path when one meter is used. The cable length is found assuming a velocity of propagation for the pulse based on nominal physical properties of the type of cable used.
Use of such meters involves disruption to the network, as each cable is disconnected then reconnected. Furthermore, apart from the time taken by the meters to test each cable, the time taken for the physical disconnection and reconnection can be considerable, especially for a medium- to large-size LAN comprising many hundreds or even thousands of cables. Measurements made on the cables while they are disconnected from the network do not necessarily provide a good measure of the performance of a link formed by one or more of the measured cables. For example, reconnecting the cable(s) back into the network to re-form the link may create one or more poor connections, so that signal degradation over the link is higher than would be expected from the cable measurements.
It is an object of the present invention to provide methods and apparatus for measuring an aspect of the performance of a link within a network without the necessity of removing the link from the network. Preferably, the aspect that is measured comprises an effective length of the link.
It is a further object of some aspects of the present invention to provide methods and apparatus for measuring the performance of a link within a local area network while the link is transmitting data.
It is a yet further object of some aspects of the present invention to provide methods and apparatus for locally or centrally measuring the performance of a link within a local area network.
In preferred embodiments of the present invention, a network, preferably a local-area network (LAN), comprises a link terminated at a first end by a data signal transmitter and at a second end by a data signal receiver. The receiver processes signals received from the transmitter in order to improve recovery of the signals from degradation due to transmission over the link. Coefficients generated by the receiver in order to perform the processing are used by a link length estimator (LLE) within the network to calculate an effective length of the link providing the signals. The effective length (as explained above in the Background of the Invention) is a measure of the attenuation generated within the link. For a link attenuating at the nominal attenuation of the link, the effective length is equal to the physical length of the link.
In some preferred embodiments of the present invention, the receiver processes the signals using an adaptive equalization technique, whereby equalization coefficients in a filter of a receiver, most preferably comprising a forward equalizer and a decision feedback equalizer, are adaptively set in order to optimize recovery of the received signals. The equalization coefficients thus determined are used by the LLE to determine the effective link length. U.S. patent application Ser. No. 09/070,466, which is assigned to the assignee of the present invention and which is incorporated herein by reference, describes a filter which uses such a technique.
Thus, the effective length of the link (and the physical length if so desired) may be measured without disconnecting the link from the network and without disruption of network operation, unlike methods known in the art which disconnect the link and so disrupt network operation. Furthermore, since the link is not disassembled while measurements are made, there is no possibility of introducing problems into the network on reassembly of the link. Measuring the performance of a network, by measuring effective lengths of links within the network without removing the links, significantly speeds up maintenance and diagnosis of problems of networks, compared to maintenance and diagnosis methods known in the art. Furthermore, effective length measurements may be made and tracked over time, without disturbing network operation, in order to detect network problems earlier and with improved precision, and thus to minimize network faults and down-time.
In some preferred embodiments of the present invention, the LAN comprises a plurality of workstations connected to one or more hubs of the network, as is known in the art. Each hub comprises a plurality of receivers and at least one LLE, which LLE measures an effective length of the link to which each receiver is connected, preferably by polling the coefficients of each receiver and calculating the effective lengths of the respective links in turn. Preferably, one of the workstations in the network is used as a network administrator station, and the station is able to read each effective length calculated by each LLE, and thus form a picture of the state of links within the network.
In an alternative preferred embodiment of the present invention, each of the workstations within the LAN comprises a receiver containing an LLE. Each LLE makes a measurement of an effective length of the link to which it is connected, and the measured effective length is read by the workstation containing the LLE. Thus each workstation is able to check the state of the link connecting the workstation into the LAN.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for determining a measure of the length of a link between a transmitter and a receiver within a communication network, including:
conveying signals from the transmitter to the receiver in accordance with normal network operation; and
processing the received signals to determine the measure of the length, responsive to a length-dependent effect of the link on the signals.
Preferably, processing the signals includes generating filter coefficients, wherein the signal is filtered using the coefficients so as to compensate for degradation of the signal due to the link length, and computing the measure based on the coefficients.
Preferably, generating the filter coefficients includes generating coefficients for adaptive equalization of the signal.
Preferably, generating the filter coefficients includes using a process of forward equalization to generate the coefficients.
Preferably, processing the received signals includes finding a solution of one or more parametric equations having the one or more filter coefficients as parameters of the one or more equations.
Alternatively, finding the solution includes transforming a function of the coefficients to the frequency domain.
Further alternatively, processing the received signals includes utilizing a substantially linear portion of the solution of the one or more parametric equations and one or more predetermined empirical constants dependent on a property of the link in order to determine the measure.
Preferably, processing the received signals includes polling the one or more filter coefficients substantially without interfering with the communication network.
Preferably, processing the received signals includes receiving the signals in a central unit of the network.
Preferably, processing the received signals includes receiving the signals in a workstation coupled to the network and reading the measure of the length of the link in the workstation.
Alternatively, the measure of the length of the link includes an effective length of the link, which is a generally linear function of a physical length of the link.
Further alternatively, the effective length is determined by comparing an actual attenuation of the link to a nominal attenuation of the link.
Preferably, conveying signals includes transmitting the signals according to an Ethernet lOOBASE standard.
Preferably, processing the received signals includes calculating an actual attenuation of the cable.
Preferably, the measure of the length is determined substantially without disconnecting any network link.
There is further provided, in accordance with a preferred embodiment of the present invention, apparatus for determining a measure of the length of a link within a communication network, including:
a receiver, which receives signals conveyed from a transmitter in the network in the course of normal network operation; and
an estimator which processes the received signals to determine the measure of the length, responsive to a length-dependent effect of the link on the signals.
Preferably, the receiver includes a filter, which generates coefficients and filters the signal using the coefficients so as to compensate for degradation of the signal due to the link length, and wherein the estimator computes the measure based on the coefficients.
Preferably, the coefficients include adaptive equalization coefficients.
Alternatively, the adaptive equalization coefficients include forward equalization coefficients.
Preferably, the estimator includes a processor which processes the received signals by finding a solution of one or more parametric equations having the one or more filter coefficients as parameters of the one or more equations.
Alternatively, the processor processes the received signals by utilizing a substantially linear portion of the solution of the one or more parametric equations and a plurality of predetermined empirical constants dependent on a property of the link.
Preferably, the estimator polls the one or more filter coefficients substantially without interfering with the communication network.
Preferably, the network includes a central unit which comprises the estimator and the receiver.
Preferably, the measure of the length of the link is read from the central unit via a network administrator station.
Preferably, the network includes a workstation which includes the estimator and the receiver and wherein the measure of the length of the link is read by the workstation.
Alternatively, the measure of the length of the link includes an effective length of the link, which is a generally linear function of a physical length of the link.
Further alternatively, the effective length is determined by comparing an actual attenuation of the link to a nominal attenuation of the link.
Preferably, the signals are conveyed according to an Ethernet 100BASE standard.
Preferably, the estimator calculates an actual attenuation of the cable.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: